This invention relates to the purification of groundwater contaminated with oxygenate(s) such as alkyl ethers and tertiary butyl alcohol. This invention further relates to a method and apparatus that result in the efficient biodegradation of these compounds to carbon dioxide and water. In particular, the invention relates to the remediation of groundwater contaminated with methyl-t-butyl ether (MTBE) and other ethers using fixed beds of granular activated carbon (GAC) seeded with specific MTBE degrading bacteria cultures and to a new method of seeding said carbon beds to avoid plugging, where the required amount of culture to degrade the MTBE can be determined by a formula. Also disclosed are oxygen and nutrient delivery systems.
In response to the 1990 Clean Air Act Amendments gasoline suppliers began to blend fuels with oxygenate(s), such as alkyl ethers, particularly methyl-t-butyl ether (MTBE). MTBE often constitutes as much as 10 to 15% by volume of unleaded gasoline.
After using oxygenated fuels for about a decade, it has become apparent that the cleaner burning fuels pose distinct threats to groundwater resources. In particular, many oxygenate(s) are very soluble in water and are slow to degrade in the environment; hence they tend to accumulate in water resources once released into the environment.
Due to leaks in underground storage tanks or spills, the groundwater at many gasoline retail, distribution, and manufacturing sites is contaminated with benzene, toluene, ethyl benzene, and xylene (BTEX), as well as MTBE and other ethers. For example, MTBE has been detected in groundwater with high frequency in many states and there are well documented cases of impacts to municipal water supply wells. Due to the fact that MTBE and other ethers are characterized by the properties of high solubility in water, relatively low volatility compared to BTEX, relatively low carbon sorption coefficient, and poor biodegradability, the ethers are more easily transported in groundwater aquifers than BTEX and do not degrade through natural attenuation. While MTBE can be removed from recovered groundwater by treatment with granular activated carbon beds (GAC), it is relatively expensive compared to the treatment of BTEX because the GAC beds are subject to frequent exhaustion. Equally important, GAC is not effective at all on TBA that is found along with MTBE in contaminated groundwater.
Where groundwater contaminated with BTEX, MTBE, and other ethers is treated using activated carbon there is a need in the art for a method which reduces the need for frequent changing of the carbon bed and which also addresses the problem of degrading tertiary butyl alcohol.
In situ methods for the removal of contaminants from ground water are known. U.S. Pat. No. 5,277,518 discloses a method of in situ removal of contaminants from soil or from ground water, the method comprising the steps of establishing in situ at least one venting well comprising gas-permeable openings at an upper portion thereof and a condensate drain at a lower end thereof and removing volatile contaminants in the ground water or soil through the venting well. This reference contemplates injecting microorganisms, nutrients for the microorganisms, and oxygen. U.S. Pat. No. 5,472,294, to the same assignee, and U.S. Pat. No. 5,653,288, to the inventors of ""518 and ""294, provide improvements, including providing an oxygen-containing substance to the contaminants and enhancing lateral dispersion of injected materials.
U.S. Pat. No. 5,037,240 discloses a method of xe2x80x98in situxe2x80x99 collection and treatment of floating, sinking and dissolved contaminants in a soil environment which involves installation of wick-like drains in at least a portion of the waste site on the down-gradient side of in-ground water flow. Some of the wick drains include porous or slotted pipes and are employed for the injection of treating chemicals or reagents into the contaminated soil for treatment in place prior to normal flow into the aquifer. Some of the drains may be employed for injection of bacteria or microbes, nutrients and/or air. U.S. Pat. No. 5,054,961, to the same assignee, discloses the added feature of forming an in-ground diversionary water barrier as a boom around at least the downstream area of said soil environment. These in situ methods do not discuss the use of carbon beds. U.S. Pat. No. 5,425,598 discloses an apparatus and method for sparging ground water by developing density driven convection and promoting the physical removal and biodegradation of contaminants.
In xe2x80x9cPerformance of Fixed Bed Reactors with Two-Phase Upflow and Downflowxe2x80x9d, Iliuta, Ion, J. Chem. Tech. Biotechnol. 1997, 68, 47-56, the performance of two-phase upflow and downflow fixed bed biofilm reactors, with the biocatalyst immobilized on the porous solid support was examined with the degradation of phenol selected as the test process.
Granular activated carbon (Hereafter GAC) has been used for treatment of water and wastewater at the surface. xe2x80x9cExperiences with GAC-Fluid Bed for Bioremediation of BTEX-Contaminated Groundwatersxe2x80x9d, G. Mazewski, J. Tiffany and Hansen, Biotechnol. Ind. Waste Treat. Biorem., (Pub. 1996)333-344(1992) relates information regarding a demonstration project and a full scale remediation project to treat groundwater from an operating recovery well at a bulk storage terminal using granular activated carbons. In this work the removal of BTEX was more satisfactory than the removal of other compounds such as MTBE.
In xe2x80x9cBioreactor Treatment of MTBE and TCE In Contaminated Ground Waterxe2x80x9d, by Miller, Michael E., et al, from In Situ and On-Site Bioremediation, Pap. Int. In Situ On-Site Biorem. Symp., 4th (1997),,Vol. 5, 89-94, the authors discuss a study at the Sparks Solvent/Fuel Site (Sparks, Nev.) where ground water containing MTBE, BTEX and various chlorinated solvents is treated in two granular activated carbon-fluidized bed bioreactors operating in parallel. For the first few weeks after reactor startup, 85% of the influent MTBE was removed, however effluent MTBE concentrations soon increased, indicating that the initial removal was predominately due to sorption and MTBE removal efficiencies dropped to 10-15%. Later carbon containing unidentified MTBE-degrading cultures was added to one of the fluidized bed bioreactors and the efficiency in that reactor increased to about 75%.
In xe2x80x9cA Review of Potential Technologies for the Treatment of Methyl tertiary Butyl Ether (MTBE) in Drinking Waterxe2x80x9d, discussing a study by Anthony Brown et al., University of Southern California Department of Civil and Environmental Engineering of the Metropolitan Water District of Southern California, City of Santa Monica, the authors mention the use of GAC, along with polymeric resins and chemically modified clays, but state at page 136 adsorbability is low on GAC, adsorption capacity for MTBE is low, and frequent GAC regeneration is required. (API-National Ground Water Association xe2x80x9cPetroleum Hydrocarbons and Organic Chemicals in Ground Water: Prevention, Detection, and Remediationxe2x80x9d Conference, Houston 11/12-14/1997)
The use of bacteria or naturally occurring microbes for biodegradation is known. U.S. Pat. No. 4,493,895 discloses microbial degradation of halogenated organic compounds. U.S. Pat. No. 5,641,679 discloses biodegradation of compounds such as naphthalene, haloaromatics, benzene, etc.
U.S. Pat. No. 5,474,934 discloses aerobic biodegradation of ethers using Amycolata sp. or a mutant. U.S. Pat. No. 5,814,514 discloses the use of propane-oxidizing bacteria for degrading an alkyl ether.
K. Mo, et al. Appl. Microbiol. Biotechnol. (1997) 47:69-72 proposes isolating from activated sludge and fruit of the gingko tree three pure cultures, belonging to the genuses Methylobacterium, Rhodococcus, and Arthrobacter, that are capable of degrading MTBE.
A microbe which is said to digest MTBE is described in a newspaper article by Steve Hart in The Press Democrat, Santa Rosa, Calif., 1 August (1999).
U.S. Pat. Nos. 5,750,364 and 5,902,734 to Salanitro, assigned to Shell Oil Co., disclose mixed bacterial cultures capable of biodegrading MTBE and TBA to carbon dioxide and water. U.S. Pat. No. 5,811,010 to Salanitro, assigned to Shell, discloses aerobic degradation of t-butyl alcohol using activated sludge. These three U.S. patents are incorporated herein by reference in the entirety.
It is apparent from the art that it is more difficult to degrade MTBE and other ethers than BTEX due to the properties of the ethers. The ethers have high solubility in water, relatively low volatility compared to BTEX, relatively low carbon sorption coefficient, poor biodegradability, and are more easily transported in groundwater aquifers than BTEX. MTBE can be removed from recovered groundwater by treatment with a GAC bed, but due to the fact it is not very hydrophobic and the capacity for sorption is not as high as BTEX, it is relatively expensive to remove by this method compared to BTEX due to frequent exhaustion of the activated carbon beds. In addition, activated carbon is not effective at all on TBA which is often found along with MTBE contaminated groundwater, and is even less hydrophobic.
There is a need in the art for a method of treating groundwater contaminated with these more recalcitrant chemicals. In addition, where an activated carbon is used to assist in degradation of MTBE, there is a need for a method that reduces the need for frequent replacement of the carbon beds. Furthermore, there is a need for a method that also provides for the degradation of TBA.
In accordance with the foregoing the present invention provides a method and apparatus for degrading oxygenate(s), including, but not limited to, ethers, alkyl ethers and alkyl alcohols, particularly branched alkyl ethers/alcohols, more particularly tertiary carbon atom-containing alkyl ethers/alcohols, and still more particularly MTBE and TBA, which reduces the need for the frequent replacement of activated carbon beds and, at the same time, allows for the removal of TBA where it would otherwise have not occurred. The invention comprises:
a) Inoculating a biodegrader capable of degrading said oxygenate on an activated carbon bed through a rigid tubular instrument having a plurality of holes around the circumference of the end used for inoculation of the carbon bed; and
b) Flowing said groundwater, or other water stream contaminated with said oxygenate(s) through a structure having a top, bottom, and sides, and a predetermined volume containing said bed of activated carbon having said biodegrader inoculated thereon.
Also within the scope of the invention is supplying oxygen in the form of hydrogen peroxide and other nutrients to said bacteria.
In determining the amount of said biodegrader required to degrade said oxygenate(s) the following relationship is useful:   B  =                    (                  0.1          -          10                )            ⁢              xe2x80x83            ⁢                        (                                    C              in                        -                          C              out                                )                ·        F              A  
Where
B=dry mass of biomass degrader needed, (gm)
Gin=influent MTBE or other component influent, (mg/I)
Cout=desired effluent MTBE or other component, (mg/I)
F=flow rate of water to be treated, L/hr
A=degrader activity in mg of compound degraded/hr/gm of biomass